Abstract
Quasars accreting matter at very high rates (known as extreme Population A [xA] quasars, possibly associated with super-Eddington accreting massive black holes) may provide a new class of distance indicators covering cosmic epochs from present day up to less than 1 Gyr from the Big Bang. At a more fundamental level, xA quasars are of special interest in studies of the physics of AGNs and host galaxy evolution. However, their observational properties are largely unknown. xA quasars can be identified in relatively large numbers from major optical surveys over a broad range of redshifts, thanks to selection criteria defined from the systematic changes along the quasars main sequence. It has been possible to build a sample of about 250 quasars at low and intermediate redshift, and larger samples can be easily selected from the latest data releases of the Sloan Digital Sky Survey. A large sample can clarify the main properties of xA quasars which are expected - unlike the general population of quasars - to radiate at an extreme, well defined Eddington ratio with small scatter. As a result of the small scatter in Eddington ratio shown by xA quasars, we propose a method to derive the main cosmological parameters based on redshift-independent "virial luminosity" estimates from measurements of emission line widths, roughly equivalent to the luminosity estimates based from line width in early and late type galaxies. A major issue related to the cosmological application of the xA quasar luminosity estimates from line widths is the identification of proper emission lines whose broadening is predominantly virial over a wide range of redshift and luminosity. We report on preliminary developments using the AlIII 1860 intermediate ionization line and the Hydrogen Balmer line H-beta as virial broadening estimators, and we briefly discuss the perspective of the method based on xA quasars.
Highlights
Quasars show a rich spectrum of emission lines coming from a side range of ionic species (e.g., Netzer, 2013)
If we considered a flattened distribution of clouds with an isotropic δviso and a velocity component associated with a rotating flat disk δvK, the structure factor appearing in Equation (8) can be written as fS = 4
The inclusion of the AlIIIλ1860 has been instrumental to the extension of the Hubble diagram to redshifts 1
Summary
Quasars show a rich spectrum of emission lines coming from a side range of ionic species (e.g., Netzer, 2013). Extreme Quasars in Cosmology via Doppler effect from emitting gas virial motion, while high-ionization lines (HILs) are more affected by non-virial broadening, probably associated with a disk wind or clumpy outflows (e.g., Marziani et al, 1996; Elvis, 2000; Proga et al, 2000; Richards et al, 2011, for a variety of approaches). The relative prominence of the wind and disk component reflects the different balance between radiation and gravitation forces (Ferland et al, 2009; Marziani et al, 2010; Netzer and Marziani, 2010), and is systematically changing along the quasar main sequence (MS). The effect is most noticeable in the distinction between type-1 and type-2 (obscured) AGN (e.g., Antonucci, 1993; Urry and Padovani, 1995), but is relevant for type-1 AGN (unobscured), as the viewing angle (defined as the angle between the disk axis and the line of sight) may range between 0 and 60 degrees
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
